The invention relates to stoppers for vials, in particular for vials subjected to a controlled pressure, for example evacuated tubes of blood sampling systems.
A known blood sampling system comprises an evacuated tube closed by a stopper and an open-ended needle-holder tube slidably mounted on the tube or its stopper. This needle holder carries a hollow needle having one part protruding axially from the closed end of the holder for pricking into a vein, and another part extending axially within the holder, the latter part being encased in a loose, flexible cover or sleeve. To take a blood sample, the needle is pricked into a vein and the evacuated tube displaced until the needle pierces the membrane, so that blood is sucked into the tube.
However, in practice the use of conventional blood sampling systems often involves difficulties.
Usually, the membrane is quite thick and, just prior to taking a blood sample, when the evacuated tube is fitted into the needle holder, the inner end of the needle must be partly pricked into the membrane in order to pre-assemble the evacuated tube and the needle holder into a blood sampling unit. This is done by sliding the needle holder to a position indicated by a reference mark. However, sometimes the membrane is accidentally perforated at this stage, causing a rise in pressure in the tube which may not then be adequately filled.
After sampling, the filled tube is withdrawn by disengaging it from the needle, but this is made difficult because of the friction of the thick membrane on the needle, and the needle is liable to traumatize the vein. Moreover, the return of the flexible cover over the end of the needle is sometimes delayed, leaving the end of the needle open and allowing blood to be projected onto the head of the stopper, which creates a source of contamination.